In a career as fragmented as the mind of Split's central character, writer/director M. Night Shyamalan has gone from being hailed as the new Spielberg with his breakthrough films The Sixth Sense and Unbreakable to being shot to flames for disasters like The Last Airbender and The Happening. Split has now become one of his biggest successes, both commercially and critically. Is it the return to form we have been led to believe it is?

Well, you can breathe a big sigh of relief because the short answer is a resounding 'yes'.

Split is great fun. It's thrilling, frightening, threatening and tense, with enough scares and smarts to keep you on your seat's edge and guessing right to the end. And it has a GREAT final moment - not really one of Shyamalan's famous clever twists, more a delightfully playful and unexpected surprise.

Things get off to a bold start with little preamble, as three girls are kidnapped and held prisoner by Kevin, a man who is strange in more ways than one. Many more. About 23 more to be exact, as Kevin has multiple personality disorder. Locked up and terrified, the young girls fear the worst but react to their situation in different ways, the two close friends encouraging outsider Casey to join them in attempts to harm Kevin or escape.

Casey's life experiences though, as told in disturbing flashbacks, have prepared her for a different approach and the lessons she learnt as the child of a keen hunter start to give her an advantage over her friends. But what becomes quickly apparent is that Kevin isn't the only person inside his body. There's Hedwig, a little boy, there's posh Patricia, but only Kevin allows them their time 'in the light' .Once the girls are separated, it is Casey's ability to play one internal character off another which gives her any means of finding an escape.

Meanwhile, Kevin's visits to his long term psychiatrist reveal that a 24th character, as yet unseen, is coming. And it's called The Beast...

Split has two main settings. One is the office of Kevin's analyst, whilst the other is the underground lair where the girls are kept. With such confines, a snappy script and tense direction matter but, most of all, it's the acting which needs to engage. And engage it does. Proving that the brilliant performance she gave in The Witch wasn't a one off, Anya Taylor-Joy makes the initially awkward Casey a fantastic central figure, a former victim who isn't going to take it any more. And it's wonderful to see Broadway star (and the original Carrie's sympathetic teacher) Betty Buckley back on the big screen. But there's just no getting away from the absolute genius of James McAvoy's performance here. It's quite astonishing how quickly he manages to convey Kevin's different personas. At one point he plays one character pretending to be Kevin to throw his analyst of the scent and it's such a brilliant piece of subtle acting that we know it's happening without knowing how we know. It's awards worthy.

If the last act veers a little too much towards horror, we can forgive it, so much fun has been had along the way. Plus, that final scene is a fanboy's wet dream... no matter how much it splits the audience.